shoot a tegatana to uke's face in ai hanmi and get them to parry it
with their leading hand leading directly to ikkyo.

Why would they block it when they could simply do ikkyo to you instead of blocking? Or if they practiced some other martial art, bat your hand down, make it unable to block, and strike you?

If you are really training for martial effectiveness then you have to have a partner who will try to do this. If your technique is working they can try but they will not be successful.

But remember, in a fight nage doesn't care what technique he uses. He has no investment in HOW he ends the fight. So if an attacker is able to protect his openings against a movement, it simply results in a flow into a new technique. It doesn't mean that the attacker actually beat that technique. In a real interaction the technique that succeeds isn't usually the technique that the defender attempted first. What should happen is, if the defender gets a position of advantage, whatever the attacker does to try to defeat his techniques will lead to greater disadvantage until finally it the defender is successful in controlling the attack.